Fractured clay



3,058,671 Patented Oct. 16, 1962 3,058,671 FRACTURED CLAY Robert F. Billue, Tennille, Ga, assignor to Thiele Kaolin Company, Sandersville, Ga., a corporation of Georgia No Drawing. Filed May 18, 1959, Ser. No. 813,658 Claims. (Cl. 241-24) This invention relates to a fractured clay and a method of producing same. More specifically, this invention relates to fractured clay suitable for coating paper having markedly greater brightness than unfractured clay of substantially the same size and source, and the method of producing said fractured clay product.

The elay that is used for coating paper is graded according to its brightness, opacity-creating ability, and the brightness values referred to herein were determined in accordance with TAPPI tentative standard T 646 M-54, using a General Electric brightness meter.

Clay as mined from the ground in the United States consists of a multitude of particles of different sizes ranging from submicroscopic up. It has become convenient in recent years to refer to clay used for coating paper by identifying the percentage by weight of the particles above and below 2 microns (i.e., 2 microns equivalent spherical diameter). The most expensive coating clays usually have more than about 90% by weight of their particles below 2 microns. This clay, when unbleached, generally has a top brightness of 85-86, and a brightness of about 87 when bleached.

The majority of the coating clays have from 70-80% by weight particles below 2 microns, and the brightness of the best of these U.S. clays, when unbleached, will be from about 84-85. The coarse clays or filler clays contain about 30-50% by weight particles below 2 microns and have a somewhat lower brightness.

It has been possible to increase the brightness of US. clays by calcining them, but this process makes the clay too hard for use as a good coating clay.

In Fundamentals of Ceramics, 2nd Ed., by McNamara and Dulberg, published by Mineral Industries EX- tension Services, The Pennsylvania State University, University Park, Pennsylvania, it is reported on pages 57, 59, 63, that when clay is heated, it tends to lose water. This publication further states that it is thought that the bonds which occur between aluminum and silica are changed or destroyed at dehydration temperatures. Further, after the clay is subjected to dehydration temperatures, the ability of the clay to rehydrate is permanently lost, and the mineral will no longer take up water and become plastic. When clay is heated from 20 to 600 C., it decreases in weight because of the loss of water. Although the publication states at page 59 that no direct comparison can be drawn between chemically combined water and plasticity, clay which has been heated to about 600 C. is not plastic and is no longer a clay but is instead a mixture or compound of alumina and silica. On page 59, the book states that when clay minerals are heated above dehydration temperatures to about 900-950 0, another reaction takes place, and that although the exact reaction is not known, its character indicates that there is a reaction between A1 0 and Si0 resulting from the decomposed kaolinite.

I have found how a clay of intermediate particle size range-that is, around 70-80% below 2 microns-may be greatly increased in brightness without in any way necessitating sacrificing softness. This is done by separating coarse clay from the natural or crude clay, and then fracturing this coarse clay to produce particles within the desired particle size range, and separating the desired fractured particles from the mass produced from the fracturing step.

I end up, for example, with a clay 78% below 2 microns and having a brightness of about 88 as compared to a brightness of about 83 for particles of the same size range in the same clay as taken from the ground. While a difference of five points of brightness may seem slight to those unfamiliar with the coating clay art, this represents several times the difference in brightness between the coarsest and finest clays and for the first time permits U.S. clays of coating softness to compete with English clays in brightness.

In producing coating grade clay for the paper industry, lumps of fiocculated clay are taken from the mine and placed in a blunger along with water and a dispersant such as sodium silicate. After the mix is treated in the blunger, deflocculated clay slip is produced. The clay slip is then subjected to a series of degritting steps during which grit and mica are removed.

The degritted clay is then subjected to a separation step that separates the fine coating grade clay (e.g., 70%- by weight below two microns) from the coarse clay. This separation may be conducted in a settling tank, centrifuge, or hydro-separator. The coarse clay that is separated from the fine coating clay represents considerable waste due to an inadequate market.

The coarse clay that is separated from the fine coating clay may be further classified in a classifying tank so as to recover filler grade clay, e.g., about 30-50% by weight below two microns), thereby leaving a coarse clay fraction (e.g., about 15-20% by weight below two microns) which is generally discarded as waste. If desired, filler grade clay may also be prepared by mixing a coarse clay with finer clay particles. But in either event, there is an inadequate market for the filler grade clay and it is sold at prices well below the prices of coating grade clay.

I have discovered that clay of superior brightness, equal to English clays and calcined domestic clays, may be produced from clays (e.g., kaolin clay) that hitherto have been discarded or represent considerable waste due to an inadequate market, and when sold, sell at comparatively low prices, without necessitating calcining the clay and without producing the hardness that results from calcination. The clay that is produced by my process has markedly greater brightness and gloss then untreated particles of clay of substantially the same size and from the same source. In my process, I may use either coarse clay after removing the fines so that there are substantially no particles finer than 2 microns, or, with a little less brightening improvement, mined, coarse crude clay. However, the coarse clays that I use, irrespective of whether they are coarse crude clays or coarse clays obtained from classification, must have not more than 35% by weight particles below two microns.

Kaolin clay as it comes from the ground, and particularly with reference to Georgia clays, will contain a small percentage of impurities such as sand and mica. These impurities are normally removed in a preliminary washing operation. The residual clay, with such small percentage of impurities as cannot readily be removed, contains particles of a wide range of size and in at least two states of division.

Kaolin clay crystals are hexagonal plates which are considered to be from 12 to 24 times as wide as they are thick. Such plates are relatively rare above 3 to 5 microns, at least in clay which has been mined, blunged in order to disperse it, washed and then sedimented.

The plates in nature are frequently, if not normally, stacked one upon the other to form what are called worms or stacks. Just as it is possible to peel one sheet of mica from a block of mica occurring in nature, so it is possible to separate the adjacent plates in a stock of clay plates. The method, however, is different since the clay particles are so much finer and smaller. However, Mellor, in Inorganic Chemistry," Vol. VI, page 476, points out that these aggregates of plates may be spread out like a deck of cards fanwise if pressed between a pair of cover glasses. In doing so it is advisable to use a drop of heavy oil to lubricate the spreading.

Observations of particle size distribution in clay are made by sedimentation methods in which it is assumed that the plates act as spheres of the same diameter in re spect to their settling speed. No adequate data is available to show the effect of stacks upon the meaning of sedimentation determination; but obviously a stack 2 microns across and 2 microns thick consisting of 12 to 24 plates would be expected to settle faster than the 12 to 24 plates separated into their individual identities.

The situation is further complicated by the fact that clay has entirely different properties when it is flocculated as compared to when it is deflocculated. The difference between fiocculated and deflocculated clay can be dramatically shown. Everyone is familiar with the clingy character of clay in the ground when it has just enough water, to make it barely plastic. Such clay will normally have solids content between 50% and 70%. The addition of a single drop of a dispersing agent such as tetrasodium pyrophosphate will change a mass of such clay to a milky suspension flowing like or almost like water. lust what happens when the clay fiocculates is not known, but it is surmised that the plates or particles agglomerate under the effect of the electrical charges into some kind of clusters or aggregates. Whatever the nature of these clusters or aggregates, they can be readily broken down by the use of a dispersing agent. However, this breaking down appears to have no relationship to the stocks which are not formed or broken down by flocculation or deflocculation.

Brightness is normally measured upon the clay itself but may also be measured upon paper which has been coated with a standard weight of a standard coating composition including the clay and a binder. The brightness is read upon a General Electric brightness meter which measures the intensity of a wavelength of light, 457 m reflected at an angle close to perpendicular of the plane of the sample surface. Readings so obtained will be different from those of the clay, and may not even correspond, i.e., a high brightness clay may not produce as high a paper brightness as another clay having a little less brightness.

The gloss of clay which is also measured by the reflectance of light from paper coated with a standard weight of a standard coating composition is made at a smaller angle of reflectance and is always made commercially upon paper which has been coated and then calendered.

It was discovered a long time ago that sedimentation could be employed to separate clays to get a larger and larger proportion of small particles in the final product. Because of an agreement of a combination of early clay producers, it became the practice to define particle size range by reference to a theoretical 2 micron size. It turned out, as expected, that within practicable limits, thefiner the particle size the greater the gloss of paper treated with such clay. In fact, gloss increases were tremendous as the average particle size was reduced.

However, no corresponding marked increase occurred in brightness with the separation of the finer particles of the clay. This was rather surprising inasmuch as the British clays of small particle size had both high gloss and high brightness; but no great increase of brightness occurred with U.S. clays as the particle size from a particular source or mine was reduced by sedimentation, although there was a significant increase in gloss.

One of the first to advocate the use of sedimented clay for coating purposes was U.S. Maloney Patent 2,158,987. In his patent, Maloney also recommended the use of as much as three hours of treatment in a pebble mill as a supplement to sedimentation as a means of reducing particle size. There is no indication that such milling will accomplish any increase in brightness and Maloney did not say so. Further, the Maloney patent does not distinguish between the size of clay to be treated, or attribute any critical importance to the particle size distribution of the clay to be treated.

Various suggestions have been made for using mechanical means to disintegrate clays by one method or another. U.S. Asdell Patent 2,726,813 suggested a comminution of clay in a gaseous stream. He reported a comparable gloss but showed a reduction in the brightness of the clay itself when compared with the sedimented clay of comparable fineness.

It was early discovered that calcining clay would increase the brightness, but this calcining makes the clay unfit for many paper coating purposes, and prior to the time of the present invention no method had been discovered for appreciably increasing the brightness of a clay which would leave the clay suitable for paper coating.

As pointed out above, in Fundamentals of Ceramics," it is reported that when clay is heated, it loses water, and, at dehydration temperatures, that it is thought that the bonds that occur between aluminum and silica are changed or destroyed. Further, when the clay is heated to about 600 C. or above, it is no longer plastic.

When coarse clay is fractured in accordance with my invention, the resulting fractured clay has markedly greater brightness and gloss than unfractured particles of clay of substantially the same'size from the same crude clay. This remarkable property of increased brightness is certainly new and is entirely unexpected. Thus, my invention involves more than improving the brightness of the clay by merely reducing the size of its particles.

In practicing my invention, it is essential that the coarse clay that is to be fractured have not more than 35% by weight of particles below 2 microns. (In giving particle size herein, I refer to the effective apparent spherical diameter of the particles as determined by sedimentation means such as the Bouyoucus hydrometer or pipette analysis. While the results obtained by the use of the hydrometer will vary slightly, depending upon the preliminary treatment of the clay and other factors, the difierences between various procedures are not generally of significance so far as this invention is concerned. However, a pipette analysis is used when there is not a homogeneous mixture of particles or when there is almost no particles under a given size and it is desired to measure to that given size. The particle sizes are given for qualitative rather than quantitative guides.) This enables a comparatively high proportion of the coarse clay to be fractured and affords a better opportunity of fracturing the same particles more than once. Thus, coarse crude clays that were formerly considered too coarse to be economically minded for conventional classification procedures due to the low recovery of fine particles may now be treated in accordance with my invention, thereby producing a fractured product that may be advantageously used for coating paper. Clay having this particle size distribution may be obtained by classifying the crude clay to remove the requisite level of particles below 2 microns. Prior to fracturing, colloidal clay material of less than about 0.1 micron may be removed from the clay that is to be treated.

The coarse clay may then be admixed with water and deflocculating agent and the resulting charged fractured in a pug mill of the type shown in U.S. Millman et al. Patent 2,535,647 or a Rafton Mill such as shown in U.S. Rafton Patent 2,448,049. When a pug mill is used, the charge should contain about 75-90% by weight solids. I prefer to use a charge of about 60-65% by weight solids in the Rafton Mill.

The charge must be subjected to treatment for sutficient time to produce (i.e. fracture and recovery by classification) a fractured product having at least about 40% by weight, preferably at least about 50% by weight, clay finer than 2 microns and fracture-induced brightness that is markedly brighter than unfractured coarse clay of substantially the same size from the same source.

The percentage of coarse clay that is fractured may be measured with some degree of precision by classifying the coarse clay to the same particle size distribution as the fractured clay; the amount of clay removed from the coarse clay by this classification, as expressed as a percent of the weight of the coarse clay prior to classification, represents at least the minimum percent of clay that was fractured.

It has been noted that the fractured coarse clay that has been treated so that it has at least about 40% by weight clay below 2 microns, preferably at least about 50% below 2 microns has greater brightness and gloss and a higher viscosity than unfractured clay having the same particle size distribution from the same source. In addition, the fractured clay particles will require more casein adhesive for coating paper. Still further, it has been noted from studying several samples of fractured clay that the fractured clay particles have substantially no worms or vermicules oriented so that the plates are substantially perpendicular to the supporting plane; this was determined by an electron micrograph study that was conducted by thoroughly mixing fractured clay and water, and positioning the admixture on a horizontal supporting structure, from which readings were taken. Still further, aqueous slurries containing at least 55% by weight of my fractured coating grade clay stiifens when agitated or subjected to shearing forces. This is called dilatancy and is believed to be caused by a change from close packing, where there is sufficient water for lubrication, to a more open packing where there is too small a volume to fill the voids. It has been noted that slurries (containing at least 55% by weight solids) prepared with samples of my fractured clay showed greater dilatancy than slurriw (having the same Weight level or solids) prepared with unfractured clay having the same particle size distribution.

Example II, infra, shows that my fractured clay produces greater brightness readings than a commercial intermediate grade of coating clay having substantially the same particle size distribution. In addition, Example II shows that when fractured clay that had an initial brightness of 89.1 was calcined, the resulting product had a brightness of 9 6.3. This 96.3 value is considerably above the brightness of 90-92 which is obtainable by calcining regularly produced coating clays of the same fineness.

It should be noted that Table XIII in Example VII, infra, shows that paper that was coated with bleached fractured clay had significantly greater brightness than paper that was coated with bleached commercial intermediate grade coating clay having substantially the same particle size distribution. Similar results are shown in Table XVI in Example VIII, infra.

Example IX, infra, clearly shows: that my fractured clay has greater brightness than conventional intermediate grade coating clay having substantially the same particle size distribution; the outstanding brightness and coating properties of my fractured coating clay, as compared to intermediate grade coating clay and calcined coating clay; and that calcined coating clay is far more abrasive than my fractured coating clay.

The test data set forth in Table XIX in Example X, infra, show that: unbleached fractured clay has significantly greater brightness than unfractured clay of substantially the same particle size distribution; and bleached fractured clay has markedly greater brightness than bleached unfractured clay of substantially the same size despite the fact that the former was treated with comparatively lower levels of bleach.

The data set forth in Example XI, infra, show that the brightness of the clay increased as its particle size decreased to 0.2 micron, and that fractured clay in the ranges of 0.5-0.2 micron and 50.5 microns was brighter than unfractured clay and that the brightest fractured 6 clay fraction that was tested was in the 0.5-0.2 micron range.

EXAMPLE I Two samples were prepared from a coarse clay, one 5 of which contains substantially all of its particles above 10 microns and the other having approximately all of its particles 5 microns and larger. Both samples were obtained by repeated classification of the clay.

Each of these samples was run through a Rafton Mill at 50% solids in deflocculated state. The clay slip was sprayed from nozzles immediately adjacent to the blade into the path of the teeth of the rotating saw. A number of passes through the machine were made, as desired.

The following Table I shows the particle size distribution (expressed as percent by weight) of the samples before and after fracturing.

1 Represents all the particles under 10 microns. Represents all the particles under 5 microns.

The brightness of the 10 micron sample before treatment was 76.5. After treatment it was 84.0.

The 5 micron sample before treatment had a brightness of 75.6. After treatment it had a brightness of 82.4.

Both after-treatment brightnesses were determined upon the entire sample.

The fractured samples were then fractionated into a number of samples of different particle size ranges and again tested for brightness. The 10 micron fractured sample was classified into a fraction which had no particles above 10 microns and 72% of its particles 2 microns or below. The classified fractured sample had a brightness of 89.2.

Another classified sample of the 10 micron fractured sample had no particles above 10 microns, 87% of its particles 2 microns and below, and a brightness of 89.4.

The 5 micron fractured sample was divided into two classified groupsone of which had 62% of its particles 2 microns and below, the other of which had 84% of its particles 2 microns and below. Neither group had any particles above 10 microns. The 62%-2 micron fraction had a brightness of 88.4. The 84.0% -2 micron fraction had a brightness of 89.5.

EXAMPLE II A special composite sample was made up from the foregoing classified fractured samples of Example I with the particle sizes distributed in approximately the same 60 proportion as a sample of a commercial intermediate grade of coating clay from the same mine. These samples had about 80% of their particles below 2 microns. Coating compositions were made up from each of these (i.e., composite and commercial) samples and applied to 65 paper to provide a 6A wax pick, which required a little more casein for the fractured clay than for the normal intermediate clay. The coating weights were substantial ly the same, being 14.7 pounds per ream for the fractured clay and 14.0 pounds per ream for the other (5'00 70 sheets of paper in. x 38 in. constitute a ream). Un-

calendered gloss as measured by a Hunter meter was 6.6 for the fractured clay and 5.0 for the intermediate coating. Brightness Was 83.2 for the fractured clay coating and 76.6 for the intermediate clay coating.

Another sample of the fractured clay which had an Table II Brightness: ff; 89.1 89.9 1 90.4 2

EXAMPLE III A sample of the coarse clay fraction produced in the commercial manufacture of intermediate grade coating clay (designated as No. 3 clay by Thiele Kaolin Company) was settled repeatedly from an aqueous suspension in preparation for being fractured in a laboratory Rafton Mill. After each settling the fines were discarded that were left in suspension after a predetermined time, and the resulting coarse particles were resuspended and settied to further remove remaining fine particles. The time of settling in each case was the time for the 2 micron size particles at top of suspension to settle out in bottom of container.

The particle sizes of the coarse fraction from the repeated settlings, as shown in Table III, was treated in the laboratory Rafton Mill at about 50% solids in a deflocculated state for 5 8 passes.

Table III [Particle size before Rafton treatment] Percent plus microns 8.5 Percent 15 to '10 microns 12.0 Percent 10 to 5 microns 46.0 Percent 5 to 2 microns 30.5 Percent finer than 2 microns 3.0

The fractured sample was fractionated to recover a fraction of finer particles of which about 78.0% were finer than 2 microns. This sample of fractionated fines from the Rafton Mill-treated clay tested as follows:

Table IV [Percent recovery37.8 Particle sizeahout 78.0% finer than 2 microns] Brightness: gg 1/ ton 88.5 1 90.0 2 89.7 3 1 Sodium hydrosulphite.

EXAMPLE IV A sample of a whole coarse dry fraction that settled out in bottom of the settling tank used in thecommercial manufacture of commercial intermediate grade coating clay (designated as No. 3 clay by Thiele Kaolin Company) was used for this run. This sample was deflocculated and run through a laboratory Rafton Mill at 60.0% solids for a total of 58 passes. The following results were obtained before and after fracturing the sam- 8 This fractured sample was fractionated to recover a fraction of finer particles, which tested:

Table VI Lbs. of bleach /Ion of Clay Brightness 86.4 87.3 87.7 87.7

1 Sodium hydrosulphite. Particle size:

Percent plus 10 microns 0.0 Percent 10 to 5 microns 2.0 Percent 5 to 2 microns 20.0 Percent finer than 2 microns 78.0 Percent recovery 52.8

EXAMPLE V A sample of the coarse clay fraction produced in the commercial manufacture of intermediate grade coating clay (designated as No. 3 clay by Thiele Kaolin Company) was settled repeatedly from an aqueous suspension in preparation for running through a laboratory Rafton Mill. After each settling, the fines were discarded that were left in suspension after a predetermined time and the resulting coarse particles resuspended and settled to further remove remaining fine particles. The resulting coarse fraction from the repeated settlings was treated in the laboratory Rafton Mill at about 50% solids in a deflocculated state for 'a total of 5 8 passes. The following results were obtained before and after fractionating the sample:

Table VII Before After fracturing fracturing Particle size:

Percent plus 15 microns. 3.0 1.0

Percent 15 to 10 microns. 14. 0 2.0

Percent 10 to 5 microns. 59.0 20. 0

Percent 5 to 2 microns... 20. 0 39. 0

Percent finer than 2 microns" 4. 0 38. 0 Brightness 73.0 80. 0

The fractured sample was fractionated to recover a fraction of finer particles, of which about 78.0% was less than 2 microns. This fraction of finer particles tested:

Table VIII Brightness 88.2 (unbleached). Recovery 49.7%.

EXAMPLE VI A sample of crude clay that tested 66% finer than 2 microns was settled repeatedly until substantially all clay finer than 2 microns was removed. The resulting coarse fraction was put through a laboratory Rafton Mill at 59.4% solids in a deflocculatcd state for a total of 58 obtained:

TableX Brightness Percent Percent finer than 2 lbs. of recovery 2 microns Without bleach 1 bleach per ton of clay 1 Sodium hydrosulphite.

EXAMPLE VII A sample of the whole coarse clay fraction produced in the commercial manufacture of intermediate grade coating clay (designated as No. 3 clay by Thiele Kaolin Company) that settled out in the bottom of the settling tank was put through a laboratory Rafton Mill at 55.0% solids in a defiocculated state for a total of 80 passes. This tested as follows:

Table XI Before After fracturing fracturing Particle size:

Percent plus 15 microns 8. O 1.0

Percent 15 to 10 microns 14. 0 3.0

Percent 10 to 5 microns..- 31.0 16.0

Percent 5 to 2 microns 33. 0 30.0

Percent finer than 2 microns 14. 0 50.0 Brightness 78. 6 82. 6

The fractured clay was classified and tested as follows:

Table XII Brightness Percent Percent finer than 2 lbs. of recovery 2 microns Without bleach 1 bleach per ton of clay 1 Sodium hydrosulphite.

Coated sheets were prepared with clay fractions of 74.0% finer than 2 microns with two pounds of sodium hydrosulphite bleach and with commercial intermediate grade coating clay of a fineness of 81% finer than 2 microns (designated as No. 3 clay by Thiele Kaolin Company) having a brightness of 86.3. The following data were obtained with these sheets.

Table XIII Parts Gt. Brightcasein Coating clay used Gloss weight Wax ness used per 100 parts clay Commercial intcrme- 8.0 12.3 Slight 4--. 78.9 10

diate grade coating clay.

74% minus2iractions 9.0 12.1 do 82.8 13

treated with 2 lbs. of

bleach 1 per ton of clay.

1 Sodium hydrosulphite.

2 Casein is the bonding agent for the clay.

EXAMPLE VIII The sample of whole coarse clay used in Example VII was repeatedly settled to remove substantially all particles finer than 2 microns and put through a laboratory Rafton Mill for a total of 80 passes at 58.2% solids in 10 a deflocculated state. The following particle size distribution resulted:

Table XIV Before After fracturing fracturing Particle size:

Percent plus 15 microns 17.0 1.0

Percent 15 to 10 microns. 18.0 6.0

Percent 10 to 5 microns 35.0 23.0

Percent 5 to 2 microns... 26.0 ,32. 0

Percent finer than 2 microns 4. 0 38.0 Brightness 77. 5 82. 0

The fractured sample which was classified tested as follows:

Table XV Brightness Percent finer Percent than 2 4 lbs. of recovery microns 0 2 3 bleach 1 per ton of clay 1 Sodium hydrosulphite.

Coated paper sheets were made with a clay fraction having 78.0% finer than 2 microns with 2 pounds of sodium hydrosulphite bleach and with commercial intermediate grade coating clay of substantially the same size (designated as No. 3 clay by Thiele Kaolin Company) having a brightness of 86.5. The following data were obtained with these sheets:

1 Sodium hydrosnlphite. I Casein is the bonding agent for the clay.

EXAMPLE IX Tests were conducted with three clay samples produced from the same clay deposit and which were properly designated as calcined clay, intermediate grade coating clay (designated as No. 3 clay by Thiele Kaolin Company), and fractured clay fines (clay articles of which about are finer than 2 microns).

The calcined clay sample was taken from a commercial run by Burgess Pigment Company, Sandersville, Georgia. This clay was made by heating pulverized coating clay at temperatures of about-1750-1850 F. The calcined clay and intermediate grade coating clay samples were representative of these clays as supplied in commercial practice. The intermediate grade coating clay and fractured clay fines had substantially the same particle size distribution. The fractured clay fines were produced with a laboratory Rafton Mill. I

The brightness value of the calcined clay and fractured clay fines was found to be 90.0, whereas the brightness value of the conventional intermediate grade coating clay was 86.0.

Paper samples were prepared by coating separate uncoated paper sheets with the calcined clay, intermediate grade coating clay, and fractured clay fines, respectively. The clays were applied to the uncoated paper of each of 11 said samples with just enough adhesive to hold the clay to the papers, and by applying a heavy coat and using the same solids make-up and applicator in each instance. As is well recognized in the clay and paper arts, and as sub- 12 Based on the test data produced in this example, wherein the brightness values of classified and conventional samples having substantially the same particle size distribution were compared, the following results were obstantiated by these test samples, the abrasive properties of tained: the calcined clay were considerably greater than the in- (1) Table XIX, supra, shows that the unbleached fractermediate grade coating clay. Similarly, the calcined tured sample had significantly greater brightness than the clay was considerably more abrasive than the fractured unbleached conventional sample. clay fines. (2) Further, the bleached fractured samples had signi- EXAMPLE X ficantly greater brightness than the bleached conventional A sample of kaolin clay slip (defiocculated clay-water Samples despite the feet that the former Samples Were mix) from a production run was introduced into a seditreated with comparatively towel" levels of bleach mentation tank. After the sedimentation tank was filled The foregoing data and results of this example Clearly d th l was l ifi d to a commercial grade, 3 Sample establish that the fractured clay has greater brightness was taken from the suspended fraction and was designated than uhfrachh'ed Clay of shhstahhahy the Same Particle as th conventional l size distribution. The outstanding brightness of the frac- A second Sample was taken f h Settled Coarse f tured clay is based upon the initial treatment (fracturing) tion resulting from this classification in the sedimentation of Coarse y having not more than 35% by Weight P tank. This coarse fraction was treated to remove subtides below tWO thiemhe- The foregoing fracturing P stantially all of the particles finer than two microns by 29 enables one to use a comparatively high Proportion of reu pendi g th l i water i a defl l t d State, clays that are too coarse to be used in conventional classettling, and removing and discarding the fines. The re- Sifieattoh Procedures d to the comparatively low recovsulting coarse fraction was treated in a laboratory Rafton ery 0t fine Particles that normally result therefrom- Mill at 56.6% solids in a defiocculated state for 58 passes. Thus, in conclusion, when coarse y 1s fractured m This treated slip was then classified to recover a relatively accordance with the above Procedure, the l'eellltlflg freefine fraction of fractured particles. This classified fractured y has markedly greater brightness than tured sample was designated as h fra tured Sample], tured particles of clay having substantially the same size Table XVII, infra, shows the particle size distribution distribution of the clay before and after it was classified, whereas EXAMPLE XI Table XVIII, infra, shows the particle size distribution of 3D A sample was l t d fr an intermediate grade the y before and t the materlat e t 1n t coating clay (designated as No. 3 clay by Thiele Kaolin laboratory Rafton Mill, and the particle size distribution company) A seccnd sample w prepared by passing 0f the above referred to fractured samplecoarse clay through a Rafton Mill and classifying the T bl XVII fractured sample. The particle size distribution of these samples and their brightness values are shown in Table Particle size distribution based on Before scdi- After scdi- XX Infra percent by weight mentation mentation Table XX tank, percent tank, percent Plus 15 microns 3. 0 0, 0 40 Unbleached Percent clay below }3 :8 0 0 Sample brightness crons--- 12.0 3.0 5 mi- 3rni 2mi- 1 m1- 0.6 mig f ei th gg icrons crons crons crons cron Commercial Table XVIII intermediate grade coating clay 84. 6 99 94 85 69 57 Pa ticle size dist ibution has d l it l i t cmsfiified ghhthifeel r on percent hy weight 8 perch t peicezi t g c e nt ay 8 99 94 31 44 Plus 15 microns.-. 7.0 2.0 0.0 50 Table XX, supra, shows that the fractured clay was is :8 $5, 55,113? $8 2:8 9:8 brighter than the intermediate grade clay. The samples 5to2microns 24.0 34.0 16.0 shown in Table XX, supra, were classified and the frac- Fmerthanzmlmns tions of less than 0.5 micron were removed therefrom.

Lbs. of sodium hydrosulphite Brightness of conventional sample--. 84. 8 86. 2 86.0 85.8

Lbs. of sodium hydrosulphite per ton of clay Brightness of fractured sample 87. 2 88. 2 88.7 88.9

The separated fraction of each sample was again classified into two smaller fractions, one of which had a particle size distribution of 0.5-0.2 micron and the other had a particle size distribution of less than 0.2 micron. The brightness values of these fractions below 0.5 micron are shown in Table XXI, infra.

A comparison of the brightness values set forth in Tables XX and XXI, supra, shows that: the 0.5-0.2 micron fractions of the fractured clay and intermediate grade clay are brighter than the samples from which they were taken; the fractured clay in the 0.5-0.2 micron range is 13 brighter than the intermediate grade clay in the same range; and the particles below 0.2 micron of each sample have materially lower brightness values than the samples shown in Table XX from which they were taken and the corresponding 05 0.2 micron samples.

Table XXII, infra, shows the brightness of the samples shown in Table XX after the particles below 0.5 micron were removed and compares these values with the values shown in Tables XX and XXI.

Table XXII Brightness of samples Brightness Brightness of Table XX of fraction Sample of samples after removal between of Table XX of clay 0.5-0.2

below 5 micron micron Commercial intermediate grade coating clay 84. 6 83.0 85. 5 Classified fractured clay. 87. 8 88. 1 88. 3

Tables XXI and XXII, supra, show that the brightness of the clay increased as its particle size decreased to 0.2 micron, and that fractured clay in the ranges of 0.5-0.2 micron and 5-0.5 microns was brighter than unfractured clay and that the brightest fractured clay fraction that was tested was in the 0.50.2 micron range.

EXAMPLE XII Table XXIII Particle size distribution: Percent by weight Plus 15 microns 9.0 15 to 10 microns 13.0 10 to 5 microns 45.0 5 to 2 microns 27.0 Finer than 2 microns 6.0

Water was added to the coarse fraction to form a slurry of about 80% solids in a defiocculated state. This slurry was treated in a pug mill of the type shown in Millman et al. Patent 2,535,647 for thirty minutes. The particle size distribution after treatment is shown in Table XXIV, infra.

Table XXIV Particle size distribution: Percent by Weight 1 Plus microns 4.0 15 to 1 0 microns 6.0 10 to 5 microns 27.0 5 to 2 microns 27.0 Finer than 2 microns 36.0

1 After pug mill treatment.

The clay from the pug mill was fractionated to recover a finer fraction having the particle size distribution shown in Table XXV, infra.

Table XXV Particle size distribution Percent by weight 1 Plus 15 microns 0.0 15 to 10 microns 0.0 10 to 5 microns 1.0 5 to 2 microns 15.0 Finer than 2 microns 84.0

ti After pug mill treatment and fractionation to finer frac- Table XXVI Lbs. of sodium hydrosulphite per ton of clay Brightness of clay shown in Table XXV 88.2 88.5 88.6

This application is a continuation-in-part of my copending application Serial No. 611,757, filed September 24, 1956, now abandoned.

The phrase fracturing by milling in the claims refers to the fracturing of kaolinitic clay particles by milling, such as is eifected, for example, by the use of pug mills (kneading) and Rafton mills (impact and/or shear) of the type shown in US. Patents 2,535,647 and 2,448,049, respectively, wherein the particles are subjected to rupturing or shearing forces which cause the kaolinitic clay particles that are treated (i.e., not more than 35% by weight finer than 2 microns) to have an increase of particles finer than 2 microns and greater brightness on the brightness scale as compared to unfractured clay of substantially the same particle size.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

l. The method of treating coarse kaolinitic clay comprising: fracturing by milling coarse kaolinitic clay having not more than 35% by wcighhparticles below 2 microns, which includes breaking discrete vermicules thereof, to obtain clay particles having at least about a 15% by weight increase of clay particles finer than 2 microns, classifying said fractured clay to recover a fraction having an increased proportion of clay particles finer than 2 microns, said fraction having at least about 40% by weight particles finer than 2 microns and having fracture-induced brightness that is markedly greater on the brightness scale than the brightness of unfractured kaolinitic clay of substantially the same particle size and from the same source.

2. The method of treating coarse kaolinitic clay comprising: fracturing by milling coarse kaolinitic clay having not more than 35% by weight particles below 2 microns, which includes breaking discrete vermicules thereof, to obtain clay particles having at least about a 15% by weight increase of clay particles finer than 2 microns, classifying said fractured clay to recover a fraction having an increased proportion of clay particles finer than 2 microns, said fraction having at least about 67% by weight particles finer than 2 microns and having fracture-induced brightness that is at least about 0.5 greater on the brightness scale than the brightness of unfractured kaolinitic clay of substantially the same particle size and from the same source.

3. The method of treating kaolinitic clay particles comprising: removing a desired amount of small particles from crude kaolinitic clay and retaining coarse clay having not more than 35% by weight clay particles below 2 microns, fracturing by milling said retained coarse clay to obtain at least about a 15 weight increase in clay particles finer than 2 microns, classifying said fractured clay to recover a fraction having an increased proportion of clay particles finer than 2 microns, said fraction having at least about 40% by weight particles finer than 2 microns and fracture-induced brightness that is at least about 0.5 greater on the brightness scale than the bright- 15 ness of unfractured particles of kaolinitic clay of substantially the same particle size and from the same source.

4. The method of treating kaolinitic clay particles'comprising: removing a desired amount of small particles from crude kaolinitic clay and retaining coarse clay having not more than 35% by weight clay particles below 2 microns, fracturing by milling said retained coarse clay to obtain at least about a 15% weight increase in clay particles finer than 2 microns, classifying said fractured clay to recover a fraction having an increased proportion of clay particles finer than 2 microns, said fraction having at least about 67% by weight particles finer than 2 microns and fracture-induced brightness that is at least about 0.5 greater on the brightness scale than the brightness of unfractured particles of kaolinitic clay of substantially the same particle size and from the same source.

5. The method of treating kaolinitic clay particles comprising: removing undesired small particles from crude kaolinitic clay and retaining coarse clay having not more than 35% by weight clay particles below 2 microns, fracturing by milling said retained coarse clay, which includes breaking discrete vermicules thereof, to obtain at least about a 15% weight increase in clay particles finer than 2 microns, classifying said fractured clay to recover a fraction having an increased proportion of clay particles finer than 2 microns, said fraction having (a) at least 67% by weight clay particles finer than 2 microns, (b) fracture-induced brightness that is at least about 0.5 greater on the brightness scale than the brightness of unfractured particles of ka'oli nitic: clay of substantially the same particle size and from the same source, and (c) substantially no vermicules oriented so that the plates are substantially perpendicular to the supporting plane.

References Cited in the'file of this patent UNITED STATES PATENTS 1,999,773 McMichael Apr. 30, 1935 2,158,987 Maloney May 16, 1939 2,305,404 Brown Dec. 15, 1942 2,710,244 Bertorelli June 7, 1955 2,920,832 Duke Jan. 12, 1960 FOREIGN PATENTS 736,094 Great Britain Aug. 31, 1955 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 6, pp. 476, Longmans, Green and Co., N.Y.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,058,671 October 16, 1962 Robert. F, Billue It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 26, for "clay, e.g. read clay (e.g. line 70, for "stock" read stack column 3, line 22, before "solids" insert a same line, for "50%" read 60% line 32, for "stocks" read stacks column 4, line 3, for 'size" read sizes 3 line 52, for "minded" read mined line 64., for charged read charge line 72, for 'recovery" read recover column 5, line 36, for "or solid" read of solid Signed and sealed this 29th day of October 1963.

(SEAL) Attest:

ERNEST We SWIDER EDWIN L, REYNOLDS Attesting Officer Ac ting Commissioner of Patents 

1. THE METHOD OF TREATING COARSE KAOLILNITIC CLAY COMPRISING: FRACTURING BY MILLING COARSE KAOLINITIC CLAY HAVING NOT MORE THAN 35% BY WEIGHT PARTICLES BELOW 2 MICRONS, WHICH INCLUDES BREAKING DISCRETE VERMICULES THEREOF, TO OBTAIN CLAY PARTICLES HAVING AT LEAST ABOUT A 15% BY WEIGHT INCREASE OF CLAY PARTICLES FINER THAN 2 MICRONS, CLASSIFYING SAID FRACTURED CLAY TO RECOVER A FRACTION HAVING AN INCREASED PROPORTION OF CLAY PARTICLES FINER THAN 2 MICRONS, SAID FRACTION HAVING AT LEAST ABOUT 40% BY WEIGHT PARTICLES FINER THAN 2 MICRONS AND HAVING FRACTURE-INDUCED BRIGHTNESS THAT IS REMARKEDLY GREATER ON THE BRIGHTNESS SCALE THAN THE BRIGHTNESS OF UNFRACTURED KAOLINITIC CLAY OF SUBSTANTIALLY THE SAME PARTICLE SIZE AND FROM THE SAME SOURCE. 